The proposed research activities involve studies on the structure, maintenance and expression of plasmid DNA in the genus Streptococcus. Emphasis will be placed on a Streptococcus faecalis strain containing two plasmids related to cellular resistance to tetracycline, kanamycin and streptomycin. Characterization of a possible gene-amplification response in relation to growth of cells in subinhibitory concentrations of tetracycline will be carried out. Additional studies will deal with the possibility that M-protein in Streptococcus pyogenes may be plasmid-borne.